In Vitro Anticancer and Proapoptotic Activities of Steroidal Glycosides from the Starfish Anthenea aspera

New marine glycoconjugates—the steroidal glycosides designated as anthenosides V–X (1–3)—and the seven previously known anthenosides E (4), G (5), J (6), K (7), S1 (8), S4 (9), and S6 (10) were isolated from the extract of the tropical starfish Anthenea aspera. The structures of 1–3 were elucidated by extensive NMR and ESIMS techniques. Glycoside 1 contains a rare 5α-cholest-8(14)-ene-3α,7β,16α-hydroxysteroidal nucleus. Compounds 2 and 3 were isolated as inseparable mixtures of epimers. All investigated compounds (1–10) at nontoxic concentrations inhibited colony formation of human melanoma RPMI-7951, breast cancer T-47D, and colorectal carcinoma HT-29 cells to a variable degree. The mixture of 6 and 7 possessed significant anticancer activity and induced apoptosis of HT-29 cells. The molecular mechanism of the proapoptotic action of this mixture was shown to be associated with the regulation of anti- and proapoptotic protein expression followed by the activation of initiator and effector caspases.